A hybrid vehicle equipped with an engine and a motor as drive sources is provided with the storage battery such as a battery for supplying power to the motor and for storing electric power generated by the motor. In the hybrid vehicle having such a configuration, it is general to perform voltage control of the motor focusing on efficiency of an inverter for driving the motor (refer to the patent documents 1 to 6, for example).    Patent Document 1: Japanese Patent No. 3746334 Publication    Patent Document 2: Japanese Laid-Open Patent Application No. 2001-275367 Publication    Patent Document 3: International Publication No. 03/056694 pamphlet    Patent Document 4: Japanese Laid-Open Patent Application No. 2005-341698 Publication    Patent Document 5: Japanese Laid-Open Patent Application No. 2005-168140 Publication    Patent Document 6: Japanese Laid-Open Patent Application No. 2002-171606 Publication